Method of controlling electronic controlled thermostat

ABSTRACT

An electronically controlled thermostat control method is obtained which makes it possible to eliminate the response delay from the time that the required cooling water temperature is set to the time that the actual cooling water temperature reaches the set water temperature by controlling the flow rate, and to realize high cooling water temperature tracking characteristics with a high degree of precision at a low cost. 
     The method of the present invention is characterized in that in an electronically controlled thermostat which is used to control the cooling water temperature of an engine, and which comprises an actuator that can arbitrarily vary the degree of valve opening without depending only on the actual cooling water temperature, the actuator is controlled by the control controller, which has means for calculating the elapsed time from the powering of the actuator to the variation of the water temperature for predicting the water temperature after the elapsed time when the cooling water temperature is controlled to an arbitrarily set water temperature, and the actuator is controlled in advance in accordance with the above-described predicted water temperature.

TECHNICAL FIELD

The present invention relates to an electronically controlled thermostatcontrol method for which allows the arbitrary variation of the degree ofvalve opening without depending on the actual temperature alone in anengine cooling water temperature control system which variably sets thecooling water temperature in accordance with the load of an engine usedin an automobile or the like (hereafter referred to as an “engine”).Included is, for example, a system in which a temperature sensing partdisposed in a heat-sensing part, and a system in which a valve iscontrolled by a motor.

BACKGROUND ART

In automobile engines, water cooling type cooling systems using aradiator are generally used in order to cool the engine. Conventionally,furthermore, in cooling systems of this type, a control valve, e.g., athermostat, which controls the amount of cooling water that iscirculated on the radiator side so that the temperature of the coolingwater that is introduced into the engine can be controlled, has beenused in order to improve the fuel consumption of the automobile.Thermostats that use a thermal expansion body as an actuator forcontrolling the valve, thermostats that depend on electronic control andthe like are known as such thermostats.

Such thermostats are devices which can control the temperature of thecooling water to a specified state by interposing a valve part in aportion of the cooling water passage, closing this valve part andcirculating the cooling water through a bypass passage without passingthe cooling water through the radiator in cases where the cooling watertemperature is low, and opening this valve part so that the coolingwater is circulated through the radiator in cases where the coolingwater temperature is high

It is generally known that an improvement in automobile fuel consumptioncan be achieved by lowering the cooling water temperature in cases wherethe automobile engine is operated under a high load, and raising thecooling water temperature in the case of a low load.

Under such conditions, electronically controlled valves, i.e.,electronically controlled thermostats, have been used in recent years inorder to provide the optimal water temperature for improving the fuelconsumption of automobiles. Such electronically controlled thermostatsare devices which control the cooling water temperature by arbitrarilycontrolling the degree of opening of the valve part, and controlling thecooling fan that is attached to the radiator, and which can thus performappropriate control of the cooling water temperature. The reason forthis is that the control device (engine control module) that variablycontrols the abovementioned electronically controlled thermostat canperform a control action while also obtaining various parameters in theengine control unit, e.g., detected information such as the coolingwater temperature, outside air temperature, vehicle speed, engine rpm,degree of opening of the throttle and the like.

Various devices have been proposed in the past as devices that canachieve an improvement in fuel consumption by performing such coolingwater temperature control under specified conditions.

For example, electronically controlled thermostats which are devised sothat a heat-radiating element is mounted in the temperature sensing partof the thermostat, and quick heating of the cooling water during enginestarting and an improvement in the fuel consumption of the engine areachieved by using heat radiation control of this heat-radiating elementin combination, have already been proposed in the past (for example, seeJapanese Patent Application Laid-Open No. 2001-317355).

As was described above, problems that must be considered whencontrolling the cooling water temperature in an electronicallycontrolled thermostat include the “response characteristics from thesetting of the powering of the actuator to the variation in the watertemperature”.

Specifically, in conventional electronically controlled thermostatcontrol methods, various factors such as undershooting, overshooting,hunting, rate of heat exchange of the cooling water and the like have onthe time period extending from the powering of the actuator to theopening of the valve so that the actual water temperature shifts to thetarget water temperature; accordingly, a considerable time is requiredfor this operation.

Conventionally, furthermore, the electrical circuit used to power thePTC used as a heat generating device mounted on the abovementionedactuator has been a constant-voltage circuit; accordingly, since theresistance value of the PTC varies with the temperature, a constant heatradiation quantity cannot be ensured. For example, assuming that thepowering of the PTC is 10 W at 0° C., the powering is 5 W when thetemperature of the PTC reaches 100° C.

Furthermore, in automobiles, the following problem also arises: namely,because of individual differences in the manner in which the driverrides, the layout of the cooling water circulation system in eachvehicle, differences in thermostats and the like, it is difficult todetermine the best set water temperature for the vehicle in the designstage; accordingly, it is desirable that attention also be given to suchpoints.

The present invention was devised in light of such facts; it is anobject of the present invention to obtain an electronically controlledthermostat control method which makes it possible to overcome theabovementioned problems encountered in the past, and to obtain anelectronically controlled thermostat control method which makes itpossible to realize high cooling water temperature trackingcharacteristics with a high degree of precision at a low cost.

Furthermore, it is another object of the present invention to obtain anelectronically controlled thermostat control method which makes itpossible to supply a set water temperature that is always suited to thevehicle, and to realize optimal fuel consumption and optimal powering,at a low cost, by providing engine load judgment means or a learningfunction.

DISCLOSURE OF THE INVENTION

In order to achieve such objects, the electronically controlledthermostat control method according to one embodiment of the presentinvention is characterized in that in an electronically controlledthermostat which is used to control the cooling water temperature of anengine, and which comprises an actuator that can arbitrarily vary thedegree of valve opening without depending only on the actual coolingwater temperature, a control controller, in addition to performingelectrical powering for the purpose of actuating said actuator,calculates the elapsed time from the powering to the resulting actuationof the control actuator and variation of the temperature and the amountof water temperature variation per unit time for predicting the coolingwater temperature following the elapsed time, and controls said actuatorin accordance with said predicted water temperature.

Furthermore, the present invention is characterized in that a controlmethod that can be applied in common to various types of actuators usedin other electronically controlled thermostats is obtained.

Here, the term “control of the actuator in advance” refers to control inwhich the time required for the set temperature to reach the calculatedcontrol water temperature is calculated, the water temperature followingthe passage of this time lag is predicted, and the powering of theactuator is controlled in advance in accordance with this predictedwater temperature so that the response delay from the time that thepowering of the actuator is determined to the time that the actual watertemperature is reached is eliminated.

Furthermore, the “actuator” is an electric motor or solenoid that opensand closes the valve, or a heat generating device disposed in theheat-sensing part.

If this is done, the response delay that has been a problem in the pastcan be eliminated by performing linear control of the valve underspecified conditions that conform much more closely to actualconditions, so that the cooling water is maintained at the requiredtemperature, thus making it possible to realize high cooling watertemperature tracking characteristics with a high degree of precision ata low cost. As a result, the cooling water temperature can be[controlled] appropriately and efficiently in accordance with the loadof the engine in the engine operating conditions, and this system isalso superior in terms of response characteristics and stability of thecooling water temperature. Moreover, there is no danger of overshooting,undershooting, hunting or the like, and the cooling water temperaturecan be appropriately controlled to a high water temperature or low watertemperature. In addition, a more reliable improvement in fuelconsumption can be achieved, and this can be achieved throughoutsubstantially the entire range of operating conditions.

An electronically controlled thermostat control method according toanother embodiment of the present invention is characterized in that theabovementioned control controller comprises control that links theabovementioned actuator control to the control of auxiliary devicesattached to the abovementioned engine when the abovementioned actuatorrequires considerable powering.

If this is done, a reduction in fuel consumption as seen from thevehicle as a whole can be appropriately achieved. Here, “control thatlinks the powering of the actuator to auxiliary devices” refers tocontrol which temporarily cuts off or restricts the supply of electricpower to auxiliary devices in cases where the power consumption of theactuator comprising a PTC, electric motor or the like is large, so thatthe fuel consumption rate or engine powering would show a deteriorationdue to the considerable consumption of electric power if auxiliarydevices were also simultaneously operated.

An electronically controlled thermostat control method according to yetanother embodiment of the present invention is characterized in that theabovementioned control controller comprises control that automaticallydetermines PI control coefficients used in the control of saidelectronically controlled thermostat in accordance with the layout ofdifferent engines or cooling water circulation systems.

If this is done, thermostat control can be performed more in accordancewith actual conditions. Specifically, there is variation in the coolingsystem layouts and thermostats in the respective automobiles mountingthe thermostat of the present invention, so that the PI (or PID) controlcoefficients used in the control of the electronically controlledthermostat show individual variation. Therefore, they have to beinstalled individually since a conformity corresponding to theindividual difference is necessary. Accordingly, considering thevariation in thermostats and the like, it is advisable to perform acontrol operation that automatically calculates the abovementionedcontrol coefficients in accordance with individual differences.

An electronically controlled thermostat control method according to yetanother embodiment of the present invention is characterized in that theabovementioned control controller comprises control that cuts thepowering of the actuator in cases where the temperature differencebetween an arbitrarily set cooling water temperature and the coolingwater temperature following the application of control is equal to orless than a specified value.

If this is done, power consumption can be reduced in the control of thethermostat.

An electronically controlled thermostat control method according tostill another embodiment of the present invention is characterized inthat the abovementioned control controller comprises control that judgeswhether the driver is a person who commonly uses a high engine load or aperson who commonly uses a low engine load, and varies the set watertemperature [accordingly].

If this is done, control of the thermostat can be performed moreappropriately in accordance with actual conditions. Here, “control thatvaries the set water temperature according to the driver” isaccomplished by monitoring the variation in the engine load applied bythe driver for a fixed time period, and calculating the mean value ofthe load. Specifically, if this mean value of the load exceeds a certainfixed value, the driver is judged to be a driver who commonly uses ahigh load, and the set water temperature is lowered. On the other hand,if the mean value of the load is less than this certain fixed value, thedriver is judged to be a driver who commonly uses a low load, and theset water temperature is raised.

An electronically controlled thermostat control method according tostill another embodiment of the present invention is characterized inthat the abovementioned actuator is a WAX type thermo-element with aheat generating device attached, the abovementioned control controllerdetects or calculates the difference between the actual flow rate andtarget flow rate of the cooling water, and the abovementioned controlcontroller corrects the hysteresis in the heat radiation amount of thethermo-element and the parts that drive the abovementioned valve.

In this invention, the poor water temperature control characteristicsthat have been a problem in the past can be eliminated by performinglinear control of the valve under specified conditions that conform muchmore closely to actual conditions, so that the cooling water ismaintained at the required temperature, thus making it possible torealize high cooling water temperature tracking characteristics with ahigh degree of precision at a low cost. As a result, the cooling watertemperature can be [controlled] appropriately and efficiently inaccordance with the load of the engine in the engine operatingconditions, and this system is also superior in terms of responsecharacteristics and stability of the cooling water temperature.Moreover, there is no danger of overshooting, undershooting, hunting orthe like, and the cooling water temperature can be appropriatelycontrolled to a high water temperature or low water temperature. Inaddition, a more reliable improvement in fuel consumption can beachieved, and this can be achieved throughout substantially the entirerange of operating conditions.

Here, “correction for the amount of heat radiation of the element” is acorrection in which the amount of heat radiation from the thermo-elementinto the cooling water is predicted, and the power is increased ordecreased so that heat corresponding to this amount of heat radiation ismade up by the heat-radiating element in order to ensure that heatcorresponding to the amount of heat escaping by heat radiation issecurely absorbed by the expansion body (WAX), thus eliminating theeffects of heat radiation. If such a correction is performed, the watertemperature control characteristics such a hunting, water temperaturecontrol width and the like can be improved.

Furthermore, correction of the hysteresis in the mechanical drivingparts is performed in the following cases. For example, there is aregion in which the amount of valve opening does not change even duringswitching from an open valve to a closed valve or from a closed value toan open valve, or even if the powering is gradually increased ordecreased, as a result of hysteresis that occurs in the mechanicaldriving parts for structural reasons during the opening and closing ofthe valve. The reason for this is that time is required for theabovementioned mechanical driving parts of the valve to begin to move inrelation to the fixed side. Accordingly, a correction is performed byincreasing or decreasing the powering of the PTC by an extra amountduring the switching of the valve “from an open valve to a closed valve”or “from a closed valve to an open valve”, so that the system is notaffected by this region.

An electronically controlled thermostat control method according tostill another embodiment of the present invention is characterized inthat the abovementioned control controller has means for predicting theradiator flow rate by detecting parameters other than the radiator flowrate, such as the element lift, temperature of the heat generator,temperature of the temperature sensor or the like.

Here, “means for predicting the radiator flow rate” refers to thecalculation of the target lift amount instead of the target flow rate byfeeding back the element lift amount when the powering of the actuatoris determined. Alternatively, this refers to the calculation of thetarget temperature instead of the target flow rate by feeding back thetemperature of the heat generator of the heat generating device or thetemperature of the temperature sensor.

By doing this, it is possible to control the cooling water temperaturewith a high degree of precision without sensing the radiator flow rate.

An electronically controlled thermostat control method according tostill another embodiment of the present invention is characterized inthat the abovementioned control that corrects the abovementioned elementlift by predicting the amount of deterioration in the element lift.

By doing this, it is possible to eliminate the response delay even moredecisively, and to perform control of the cooling water temperature witha high degree of precision over a long period of time. Here, “correctionthat predicts the deterioration in the amount of element lift” refers tothe following correction: namely, as a result of deterioration of theelement over time, the water temperature control characteristicsdeteriorate compared to the initial characteristics (e.g., watertemperature hunting occurs, the water temperature control width isincreased and the like); accordingly, the amount of deterioration in thelift of the element is predicted from the amount of increase inovershooting or the difference from the initial water temperaturegradient, and the powering is increased or decreased so that the effectsof this amount of deterioration are eliminated.

An electronically controlled thermostat control method according tostill another embodiment of the present invention is characterized inthat the abovementioned control controller judges that theabovementioned electronically controlled thermostat has malfunctioned incases where the measurement of the resistance value of theabovementioned heat generating device at the time that theabovementioned engine is started indicates that the difference betweenthis resistance value and a pre-stored reference resistance value isequal to or greater than a specified value.

If this is done, the electronically controlled thermostat can beappropriately and reliably controlled.

Thus, the cooling water temperature control system of an automobileengine that includes an electronically controlled thermostat using thecontrol method of the present invention has a construction comprising anelectronically controlled thermostat with a structure that allowsarbitrary water temperature control, a water temperature sensor thatsenses the actual water temperature in the cooling water system, and acontrol controller that performs correction calculations for the purposeof controlling the cooling water to a set water temperature and thelike. This system is constructed so that a sensor that detects the flowrate in the cooling water system, a sensor that detects the lift of thethermo-element, a temperature sensor that detects the WAX orheat-radiating element used as an expansion body or the like isappropriately used.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a control block diagram of a system equipped with an Rd lowrate sensor which shows one embodiment of the electronically controlledthermostat control method of the present invention;

FIG. 2 is a schematic diagram used to illustrate the cooling watertemperature control system of an engine using the electronicallycontrolled thermostat control method of the present invention;

FIG. 3 is a control block diagram which shows a modification of thesystem shown in FIG. 1;

FIG. 4 is a control block diagram which shows a modification of thesystems shown in FIGS. 1 and 3;

FIG. 5 is a diagram which is used to illustrate the heat-generatingcircuit of the PTC;

FIG. 6 is a diagram which is used to illustrate the element heatradiation amount correction control in FIG. 6;

FIG. 7 is a graph which is used to illustrate the correction control ofthe response delay;

FIG. 8 is a diagram which is used to illustrate the feedback control ofthe predicted water temperature following the passage of the time lag;

FIG. 9 is a diagram which is used to illustrate another example of thecontrol shown in FIG. 8;

FIG. 10 is a graph which is used to illustrate the correction control ofthe hysteresis in mechanical driving parts;

FIG. 11 is a graph which is used to illustrate the power consumptionreduction control;

FIG. 12 is a graph which is used to illustrate the optimal watertemperature setting control;

FIGS. 13( a), (b) and (c) are graphs which show water temperaturecontrol images with the set water temperature varied;

FIG. 14 is a diagram which is used to illustrate the correction controlof the deterioration of the element over time;

FIG. 15 is a graph which is used to illustrate the correction control ofthe deterioration of the element over time;

FIG. 16 is a graph which is used to illustrate the detection of thedeterioration in the element lift;

FIG. 17 is a graph which is used to illustrate the learning control ofthe PI value; and

FIG. 18 is a control block diagram of a system using a flow rate controlvalve such as a butterfly valve driving by an electric motor or thelike, which shows another embodiment of the electronically controlledthermostat control method of the present invention.

EXPLANATION OF SYMBOLS

1 Automobile engine used as engine, 2 Radiator (Rd) used as heatexchanger, 3 Outflow side cooling water passage, 4 Inflow side coolingwater passage, 5 Bypass water passage, 10 Valve unit used aselectronically controlled thermostat which functions as waterdistribution valve, 11, 12 Water temperature sensors, 20 Controllercomprising control device (ECU: engine control unit), 21 Radiator flowrate sensor (Rd flow rate sensor), 22 Lift sensor, 23 PTC temperaturesensor, 24 WAX temperature sensor.

BEST MODE FOR CARRYING OUT THE INVENTION

FIGS. 1 and 2 show one embodiment of the electronically controlledthermostat control method of the present invention.

In these figures, a description will first be presented below on thebasis of FIG. 2, which shows an overall outline of the cooling watertemperature control system of an automobile engine that includes anelectronically controlled thermostat.

In FIG. 2, 1 indicates an automobile engine used as the engine [in thepresent system]; a universally known cooling water passage (not shown inthe figures) is formed inside this engine 1.

2 indicates a heat exchanger, i.e., a radiator (Rd). A universally knowncooling water passage is also formed inside this radiator 2;furthermore, the cooling water inlet pat 2 a and cooling water outletpart 2 b of the radiator 2 are connected to cooling water passages 3 and4 that circulate cooling water between [the radiator 2] and theabovementioned engine 1.

The cooling water passage is constructed from an outlet side coolingwater passage 3 that communicates between a cooling water outlet part 1b disposed in the upper part of the engine 1 and a cooling water inletpart 2 a disposed in the upper part of the radiator 2, and an inlet sidecooling water passage 4 that communicates between a cooling water outletpart 2 b disposed in the lower part of the radiator 2 and a coolingwater inlet part 1 a disposed in the lower part of the engine 1.Furthermore, a bypass water passage 5 which forms a “short-circuit”connection between the cooling water passages 3 and 4 is provided, and avalve unit 10 used as an electronically controlled thermostat thatfunctions as a water distribution valve is disposed in the confluencepart where this bypass water passage 5 joins the abovementioned coolingwater passage 4.

For example, this valve unit 10 has a construction of the type disclosedin the abovementioned Patent Reference 1 or the like. The valve isconstructed from a thermo-element with a mechanism that senses thetemperature of the cooling water and causes the extension of a piston bythe expansion of WAX that is mounted inside, a main shaft which isconnected to the tip end portion of the piston via a connecting member,and a main valve body and bypass valve body supported on this mainshaft.

Furthermore, a heat generating element is attached to the head part ofthe thermo-element in a location that does not contact the coolingwater. The valve can be controlled by powering this heat generatingelement. For example, on the basis of output signals from the controlcontroller in accordance with the engine operating conditions, the valvecan be opened early in cases where the cooling water temperature is highwhen the engine load is increased. Furthermore, control of the engineitself (such as cooling of the engine by increasing the amount of liftto an amount that is greater than usual or the like) is also possible,and the degree of opening of the valve can be arbitrarily varied withoutdepending on the actual temperature alone.

Furthermore, heat generating elements that can be used include nichromewires, PTC elements, Peltier elements and the like; such elements can beselected in accordance with the application involved.

Moreover, an engine cooling water circulation passage is formed by theabovementioned engine 1, radiator 2, cooling water passages 3 and 4 andthe like.

A water temperature sensor 11 such as a thermistor or the like isdisposed in the outflow side cooling water passage 3 near the coolingwater outflow part 1 b in the abovementioned engine 1 (here, in aportion of bypass passage 5 which is in a comparable location). Thedetection value obtained by this water temperature sensor 11, i. e.,information relating to the water temperature on the engine outlet side,is sent to the controller 20 which comprises a control device (ECU:engine control unit), so that the flow of the cooling water can beappropriately controlled in accordance with the operating conditions ofthe engine 1 and the like.

In the abovementioned cooling water passage 4 on the inflow side, awater temperature sensor 12 which detects the water temperature on theoutlet side of the radiator 2 is disposed on the upstream side of thevalve unit 10. The detection value of this water temperature sensor 12is also sent to the controller 20.

Furthermore, the system is devised so that this controller 20 alsocontrols the fan motor of a cooling fan which is attached to theabovementioned radiator 2 and used for the forcible air cooling of thecooling water.

Furthermore, although details are not shown in the figures, informationindicating the operating conditions of various parts such as the engine1, radiator 2 and the like, e. g., Ne (engine rpm), θth (degree ofthrottle opening) and the like, are also sent to the controller 20.

In the above construction, the valve unit 10 based on an electronicallycontrolled thermostat appropriately controls the cooling watertemperature in accordance with the load of the engine 1 in theautomobile operating conditions.

In the present invention, as a result of the installation of a radiatorflow rate sensor (hereafter referred to as the “Rd flow rate sensor”) 21in the inflow side cooling water passage 4 that leads from the radiator2 to the engine 1 in the abovementioned cooling water temperaturecontrol system, control of the cooling water temperature is performed asshown in FIG. 1.

Specifically, in a conventional structure, control of the cooling watertemperature is accomplished by PID (or PI) control on the basis of thetemperature difference between the cooling water passages 3 and 4. As aresult, the powering of the heat generating element (e.g., PTC) issimply controlled. Accordingly, since the variation in the powering ofthe heat generating element and the Rd flow rate on the radiator sideare not proportional, hunting occurs, and the water temperature controlwidth is increased, thus leading to the problem of poor watertemperature control characteristics. Consequently, in order to solvethis problem, the target radiator flow rate (target Rd flow rate) iscalculated by the amount of PID (or PI) control on the basis of thetemperature difference, and various corrections are added to this targetRd flow rate to achieve stabilization, so that feedback control isperformed as shown in FIGS. 1, 3 and 4.

FIG. 1 is a control block diagram of a system in which a heat generatingdevice and an Rd flow rate sensor 21 are installed in a conventionalthermostat in the actuator. Here, a heat generating element is used asthe heat generating device. Specifically, in the process of heatgeneration by the powering of the heat generating element disposedinside the thermostat, the difference ΔT between the actual watertemperature and set water temperature of the cooling water is detected,and the target flow rate is calculated by PID control. Then, after thedifference ΔQ between the actual flow rate and target flow rate isdetected, further PID control is performed so that a correction of theamount of heat radiation by the element, a correction of the hysteresisin the mechanical driving parts, a correction that suppresses powerconsumption and the like are added, and the powering of the heatgenerating element is determined. In this way, the system is constructedso that control is performed which eliminates the response delay (timelag) from the determination of the powering of the heat generatingelement to the time at which the actual water temperature is reached,and which also eliminates water temperature hunting and the like. Inthis process, the target Rd flow rate is calculated, this is comparedwith the actual Rd flow rate and adjusted, and feedback control isperformed.

Furthermore, instead of an Rd flow rate sensor, it would also bepossible to use the element lift (which allows easy prediction of the Rdflow rate), temperature of the PTC and WAX constituting the heatgenerating device or the like, and to use these values as another typeof feedback information.

Specifically, in cases where an Rd flow rate sensor 21 cannot beattached or the like, a lift sensor 22 that detects the amount of liftof the element and a PTC temperature sensor 23 or WAX temperature sensor24 that detects the temperature of the PTC or WAX are installed in thevalve unit 10 constituting the electronically controlled thermostat asindicated by the imaginary lines in FIG. 2, and the control shown inFIG. 3 or FIG. 4 is performed using these detection values.

FIG. 3 shows a case in which the abovementioned lift sensor 22 is usedto calculate the target lift amount instead of the abovementioned targetRd flow rate, and the element lift amount thus determined is fed back.

FIG. 4 shows a case in which the PTC temperature sensor 23 or WAXtemperature sensor 24 is used to calculate the target temperatureinstead of the abovementioned target Rd flow rate, and the PTC or WAXtemperature thus determined is fed back.

If this is done, sensing of the radiator flow rate, i. e., the radiatorflow rate sensor, can be eliminated.

Furthermore, in the abovementioned FIGS. 1, 3 and 4, the PID calculationresults are added and subtracted, multiplied and divided; however, itwould also be possible to alter the PID control constants instead.

In cases where a PTC is used as the heat generating element inperforming cooling water temperature control by the abovementionedsteps, it is advisable to use a constant-current circuit as the heatgenerating circuit that powers the PTC. Specifically, in cases where aPTC and WAX element (this may also be a bimetal or shape memory alloySMA) are combined with the heat generating device of the actuator in theelectronically controlled thermostat (valve unit 10), it is ideal formaintaining the amount of valve opening that it be possible to maintainthe quantity of heat that is generated by the PTC at a constant value ina structure in which the valve is opened by heating the WAX element withthe PTC.

Conventionally, however, since a constant-voltage circuit is used as thePTC powering circuit, the resistance varies with the temperature rise ofthe PTC itself even if the same voltage is applied, so that the poweringalso varies, resulting in a fluctuation in the amount of valve openingso that there is an increase in water temperature hunting and the watertemperature control width, and thus a deterioration in the watertemperature control characteristics.

Stable powering can be ensured, and control of the amount of heatgenerated by the PTC can be facilitated, by using a constant-currentcircuit as the PTC powering circuit as shown in FIG. 5, and thuscanceling the powering variation characteristics caused by the variationin the temperature of the PTC itself, in order to solve this problem.

Furthermore, in the control block diagrams shown in FIG. 1 or FIGS. 3and 4, “correction of the amount of heat radiation by the element”refers to a correction in which the amount of heat radiation from thethermo-element into the cooling water is predicted, and the powering isincreased or decreased so that heat corresponding to this amount of heatradiation is made up by the PTC in order to ensure that heatcorresponding to the amount of heat escaping by heat radiation issecurely absorbed by the expansion body (WAX), thus eliminating theeffects of heat radiation.

Specifically, in cases where the element that is heated by the PTC isdisposed in the cooling water, or a portion of the element is disposedin a position that contacts the cooling water, the heat that isgenerated is constantly radiated into the cooling water that flowsthrough the surrounding area. In cases where this amount of heatradiation is large, the amount of valve opening cannot be maintainedeven if the same powering is applied to the PTC; as a result, the watertemperature control characteristics show a deterioration. In order tosolve this problem, means for predicting the amount of heat radiationfrom the element into the cooling water are provided as shown in FIG. 6,and the powering is increased or decreased so that heat corresponding tothis amount of heat radiation can be supplemented by the PTC. As aresult, even if the amount of heat that is radiated into the coolingwater from the element increases or decreases, the effect of this on theamount of valve opening can be eliminated.

Furthermore, in this correction control of the amount of element heatradiation, the amount of heat radiation that is required in this case isextracted from an element heat radiation correction amount map withrespect to Ne, and this is added to the PTC powering. Besides a methodof simple prediction from Ne, the prediction of the element heatradiation amount can also be accomplished by performing higher-precisionpredictions using Ne and the outside air temperature, radiator outletside water temperature, engine load and the like.

Canceling control of the response delay is performed as follows:specifically, when problems such as overshooting, undershooting, huntingand the like occur as a result of such a response delay, problems interms of the durability of the water cooling system and engine parts, adeterioration in fuel consumption and the like arise. In order to solvesuch problems, it is advisable to provide means for predicting the watertemperature following the passage of the time lag, and to eliminate thetime lag (at least in approximate terms) by controlling the valve inadvance in accordance with the predicted water temperature following thepassage of the time lag as shown in FIG. 7.

Here, the “predicted water temperature following the passage of the timelag” is the water temperature used for control; if control is performedin advance using this water temperature, the PTC powering requiredfollowing the passage of the time lag can be set in advance, so thatthis powering is reflected following the passage of the time lag.

In this step, first of all, the predicted water temperature followingthe passage of the time lag is calculated from the water temperatureobtained from the sensor and the amount of variation in the watertemperature per unit time.

Here, the precision can also be further increased if the variation inthe water temperature variation is calculated.

Next, it is advisable to subject the predicted water temperature thusdetermined to PID control or the like that determines the originalamount of powering. This is shown in FIG. 8.

Furthermore, in addition to a method in which the water temperaturefollowing the passage of the time lag is predicted from the time lagtime Td (i.e., the time period extending from the alteration of thepowering to the point in time at which the water temperature is fedback), it would also be possible to detect this with higher precision byadding the variation in the radiator outlet side water temperature, theengine load or the like. For example, since the flow velocity of thecooling water is proportional to Ne, Ne can be used as a parameter inthe calculations for the variation in the time period extending from thevariation in the powering to the variation in the water temperature.Furthermore, if the time period extending from the powering variation tothe water temperature feedback is measured each time, and the time lagtime Td is determined on the basis of these values, deterioration in theelement or the like over time can also be handled. Moreover,higher-precision time lag detection means may also be used in which awater temperature sensor is disposed in the mixing [area], and the timeperiod extending from powering to the opening of the valve is measured.

In the abovementioned method, canceling of the time lag is realized bychanging the water temperature used as a control reference to thecalculated water temperature following the passage of the lag time;however, the same action can also be realized by substituting the targetwater temperature as shown below.

Next, the substitution method of this target water temperature Ts willbe described.

Specifically, the water temperature following the passage of the timelag is first calculated from the water temperature variation read infrom the sensor.

Then, as is shown in FIG. 9, this determined water temperature variationcan be subtracted from the set water temperature, and PID control can beperformed so that the value conforms to this set water temperature.

Here, it will be understood that the flow of the control process is theopposite in the case of overshooting and in the case of undershooting.

Furthermore, correction of the hysteresis in the mechanical drivingparts is performed in the following cases. For example, there is aregion (insensitive band) in which the amount of valve opening does notchange even during switching from an open valve to a closed valve orfrom a closed value to an open valve, or even if the powering isgradually increased or decreased, as a result of hysteresis that occursin the mechanical driving parts for structural reasons during theopening and closing of the valve. The reason for this is that time isrequired for the abovementioned mechanical driving parts of the valve tobegin to move in relation to the fixed side. Accordingly, it isadvisable to perform a correction by increasing or decreasing thepowering of the PTC by an extra amount (base up or base down) as shownfor example in FIG. 10 during the switching of the valve “from an openvalve to a closed valve” or “from a closed valve to an open valve”, sothat the system is not affected by this region.

Here, it will be understood that in an electronically controlledthermostat based on a system using a flow rate control valve such as abutterfly valve driven by an electric motor or the like, the elementlift variation can be established by substituting the valve variation orPTC output variation for the actuator output variation.

Furthermore, “correction that suppresses power consumption” isaccomplished by stopping the powering of the PTC (powering of theactuator or the like) in cases where the temperature difference betweenthe set water temperature and the control water temperature is equal toor less than a certain fixed value.

Specifically, in cases where the set water temperature is brought toapproximately the same temperature as the valve opening temperature ofthe thermostat, the PTC is constantly left in a powered state, so thatpower consumption increases, thus leading to an increase in fuelconsumption and a drop in output.

Accordingly, as is shown in FIG. 11, in cases where the temperaturedifference ΔT between the set water temperature and the control watertemperature is equal to or less than a certain value, the powering ofthe PTC is completely stopped. Of course, a method in which the setwater temperature is raised so that the amount of powering is reducedmay also be used.

Furthermore, in cases where cooling water temperature control isperformed using a system in which a heat generating device is disposedin the abovementioned WAX type thermostat, and the resistance valuevaries when the heat generating device is powered (e.g., a PTC, nichromewire or the like), it is advisable from the standpoint of stability tojudge malfunctioning of the thermostat by measuring the resistance valueof the PTC, nichrome wire or the like when the engine is started, anddetermining whether or not this value is within a standard range.

Furthermore, in performing such cooling water temperature control, it isdesirable from the standpoint of the overall automobile system toperform control that is linked to the auxiliary devices that areattached to the engine. Specifically, in cases where a large amount ofpowering is required by the PTC, it is advisable to perform controllinked to the auxiliary devices by adding control that cuts off theoperation of auxiliary devices such as air conditioning or the like, orthat reduces the powering of the alternator or the like. If this isdone, the fuel consumption rate and engine output can be ensured incases where considerable power is consumed, as when the PTC powerconsumption is large, auxiliary devices are simultaneously operated orthe like.

Furthermore, in performing the abovementioned cooling water temperaturecontrol, it is also necessary to judge whether the driver operating theautomobile is a person who commonly uses the high engine output regionor a person who commonly uses the low engine output region, and to varythe set water temperature [accordingly], in order to prevent adeterioration in fuel consumption or a drop in powering.

Specifically, in the case of conventional control, if the set watertemperature is set in accordance with drivers who commonly performlow-load operation, the set water temperature is increased. Accordingly,in the case of drivers who commonly perform high-load operation, boththe fuel consumption and engine output show a deterioration. The same istrue in the opposite case.

In order to solve such problems, as shown in FIG. 12 and FIG. 13, it isadvisable to perform control in which the set water temperature variesaccording to the driver. Specifically, this is accomplished bymonitoring the variation of the load in the case of a [given] driver fora fixed period of time, and calculating the mean value of the load. Morespecifically, if this mean value of the load exceeds a certain fixedvalue, the driver is judged to be a driver who commonly uses a highload, and the set water temperature is lowered. On the other hand, ifthe mean value of the load is less than this certain fixed value, thedriver is judged to be a driver who commonly uses a low load, and theset water temperature is raised.

Furthermore, both the raising width and lowering width may be madeproportional to the mean value of the load. Moreover, the shift to a lowwater temperature may be accelerated by altering the high load judgmentcriteria together with the set water temperature. Furthermore, ajudgment may also be made according to the manner of depressing theaccelerator pedal. It is conceivable that the system might also beendowed with a learning function in which this set water temperature isstored in memory, and the system is started from the same set watertemperature the next time that the engine is started.

Furthermore, in performing the abovementioned cooling water temperaturecontrol, it is also desirable to perform a correction for thedeterioration of the element lift over time. The reason for this is thata drop in the water temperature control characteristics compared to theinitial characteristics as a result of deterioration of the element overtime is unavoidable.

Accordingly, it is advisable to provide means for predicting the amountof deterioration in the lift, and to perform control with the poweringof the PTC increased so that compensation is made for this amount ofdeterioration, thus preventing a drop in lift caused by thisdeterioration in the lift. These conditions are shown in FIGS. 14, 15and 16.

Here, in cases where control is performed using a correlation table ofthe amount of powering of the PTC and amount of lift, it is advisable tocalculate the amount of correction with reference to this table.

Furthermore, in detecting the amount of deterioration in the elementlift, the difference in the amount of water temperature overshooting orthe temperature at which the water temperature again shifts to a dropafter first rising is first compared with the initial state undercertain operating conditions, the deviation of the valve openingtemperature is detected, and the amount of deterioration in the lift isderived from this. Next, under certain operating conditions, thetemperature at which the slope of the water temperature varies duringthe rise of the water temperature is compared with the initial state,the deviation of the valve opening temperature is detected, and theamount of deterioration in the lift is determined.

Furthermore, in the system that performs the abovementioned coolingwater temperature control, it is necessary to match the PID (or PI)control constants according to differences in the thermostats of therespective vehicles in which the system is mounted. It is generallyadvisable that this matching be performed in the design stage; however,considering the variation in engine cooling water systems, the variationin valves and the like, some trouble in achieving appropriate control isunavoidable. Accordingly, it is desirable to devise the system so thatthe PI control constants can be automatically determined according tothe vehicle in which the system is mounted following engine assembly,and so that automatic tuning can be performed.

In this case, as is shown in FIG. 17, the mean value of the temperaturedifferences during a fixed period of time is calculated, and theproportionality constants and integration constants are increased ordecreased so that this mean value decreases. Appropriate proportionalityand integration constants are set at the time of shipping. Furthermore,the mean temperature difference ΔT for a certain time period ismeasured, and the respective constants are preferably increased by 1.5times with respect to the proportionality and integration constants inthis case. Then, the mean temperature difference is measured again. Inthis case, if the mean temperature difference is smaller, the constantsare again preferably multiplied 1.5 times with these proportionality andintegration constants as a base. However, if the mean temperaturedifference is larger, the original values are preferably multiplied by0.65 times, and the mean temperature difference is measured, so that thetemperature difference is reduced. In this case, if the temperaturedifference is not reduced, it appears that the original values are thebest proportionality and integration constants.

Furthermore, since there may also be cases in which the optimalproportionality and integration constants vary according to individualdifferences in the thermostats and changes over time, it is desirablethat confirmation means of this type operate so that optimal values areconstantly sought.

Furthermore, the present invention is not limited to the structures ornumerical values described in the abovementioned embodiment; it goeswithout saying that the shapes, structures and the like of various partsmay be appropriately altered or modified.

Specifically, the electronically controlled thermostat to which thepresent invention is applied may have any structure as long as thisthermostat is capable of controlling the cooling water temperature to anarbitrary temperature. For example, besides WAX+PCT type thermostats orthe like, it would also be possible to use an electronically controlledthermostat based on a system using a flow rate control valve such as abutterfly valve driven by an electric motor or the like. Furthermore,the heat generating device used is not limited to a heat generatingelement; any heat generating device may be used as long as this devicecomprises a heat generator such as a nichrome wire or a heat generatorutilizing dielectric heating, induction heating, microwave heating orthe like. Furthermore, the heat generating element is likewise notlimited to a PTC; a Peltier element or the like may also be used.Furthermore, a bimetal or shape memory alloy (SMA) may be used insteadof WAX.

Here, FIG. 18 is a control block diagram showing a case in which theabovementioned butterfly valve driven by an electric motor or the likeis used. In this figure, the system is constructed so that control isperformed as follows: namely, the difference ΔT between the actual watertemperature and target water temperature of the cooling water isdetected, and the target flow rate is calculated by PID control. Then,after the difference ΔQ between the actual flow rate and the target flowis detected, PID control is performed, so that the powering of theelectric motor that opens and closes the flow rate control valve (e.g.,butterfly valve or the like) used as an actuator is determined; as aresult, the response delay from the arbitrary setting of the watertemperature of the cooling water to the point in time that the actualwater temperature is reached is eliminated. Furthermore, since the otherparts are the same as in the abovementioned FIGS. 1, 3, 4 and the like,a concrete description of these parts is omitted here.

Here, it will be understood that control that cancels the responsedelay, control that is linked to the engine auxiliary devices, controlthat provides an automatic learning function, control that varies theset water temperature according to the engine load, a correction thatreduces power consumption and a correction of the hysteresis in themechanical driving parts are effectively performed.

Furthermore, the structures of the other constituent parts and coolingwater circulation passages, and the numerical values and the likedescribed in the various parts, are not limited to the structures andnumerical values described in the abovementioned figures anddescription. Parts of various configurations may be freely used.Furthermore, the descriptions of the various types of control mentionedabove are merely examples; various configurations may be employed withinlimits that involve no departure from the spirit of the presentinvention.

INDUSTRIAL APPLICABILITY

As was described above, the electronically controlled thermostat controlmethod of the present invention makes it possible to eliminate theproblems encountered in conventional control, and to realize even highercooling water temperature tracking characteristics with a high degree ofprecision at a low cost.

Furthermore, by using a constant-current circuit as the PTC poweringcircuit, the present invention makes it possible to obtain a heatradiation quantity that is not influenced by the heat-radiating element(e.g., PTC).

Furthermore, by providing engine load judgment means or a learningfunction, the present invention can supply, at a low cost, a set watertemperature that is always suited to the vehicle, and can realizeoptimal fuel consumption and optimal powering.

1. A method for controlling an electronically controlled thermostatwhich controls a temperature of a cooling water of an engine, the methodcomprising: providing an actuator which is configured to vary a degreeof a valve opening without depending only on an actual temperature of acooling water and comprises a WAX type thermo-element, a heat generatingdevice attached to the WAX type thermo-element, a control controllerwhich performs electrical powering for actuating the actuator andcorrects a heat radiation amount of the WAX type thermo-element andhysteresis in parts that drive the actuator, and a controller whichdetects or calculates a difference between an actual flow rate and atarget flow rate of the cooling water; calculating an elapsed time fromthe electrical powering to resulting actuation of the actuator,variation of the temperature of the cooling water and an amount of watertemperature variation per unit time for predicting the temperature ofthe cooling water following the elapsed time; generating a predictedtemperature of the cooling water; and controlling the actuator inaccordance with the predicted temperature of the cooling water.
 2. Themethod according to claim 1, wherein the control controller comprises acontrol that links an actuator control to a control of auxiliary devicesattached to the engine when the actuator requires considerable powering.3. The method according to claim 1, wherein the control controllercomprises a control that automatically determines one of PID and PIcontrol coefficients used in control of the electronically controlledthermostat in accordance with a layout of different engines or coolingwater circulation systems.
 4. The method according to claim 1, whereinthe control controller comprises a control that cuts the electricalpowering of the actuator in cases a temperature difference between anarbitrarily set cooling water temperature and the temperature of thecooling water following application of control is equal to or less thana specified value.
 5. The method according to claim 1, wherein thecontrol controller comprises a control that judges whether a driver is aperson who commonly uses a high engine load or a person who commonlyuses a low engine load, and varies a set water temperature accordingly.6. The method according to claim 1, wherein the control controllercomprises means for predicting a radiator flow rate by detectingparameters other than the radiator flow rate.
 7. The method according toclaim 1, wherein the control controller comprises a control thatcorrects an element lift by predicting an amount of deterioration in theelement lift.
 8. The method according to claim 1, wherein the controlcontroller judges that the electronically controlled thermostat hasmalfunctioned in cases a measurement of a resistance value of thethermo-element at a time that the engine is started indicates that adifference between the resistance value and a pre-stored referenceresistance value is equal to or greater than a specified value.
 9. Themethod according to claim 6, wherein the control controller comprisesmeans for predicting a radiator flow rate by detecting parameters whichis at least one of an amount of element lift, a temperature of a heatgenerator, and a temperature of a temperature sensor.
 10. The methodaccording to claim 1, wherein the control controller links an actuatorcontrol to a control of auxiliary devices attached to the engine whenthe actuator requires considerable powering.
 11. The method according toclaim 1, wherein the control controller automatically determines one ofPID and PI control coefficients used in control of the electronicallycontrolled thermostat in accordance with a layout of different enginesor cooling water circulation systems.
 12. The method according to claim1, wherein the control controller cuts the electrical powering of theactuator in cases a temperature difference between an arbitrarily setcooling water temperature and the temperature of the cooling waterfollowing application of control is equal to or less than a specifiedvalue.
 13. The method according to claim 1, wherein the controlcontroller judges whether a driver is a person who commonly uses a highengine load or a person who commonly uses a low engine load, and variesa set water temperature accordingly.
 14. The method according to claim1, wherein the control controller predicts a radiator flow rate bydetecting parameters other than the radiator flow rate.
 15. The methodaccording to claim 1, wherein the control controller corrects an elementlift by predicting an amount of deterioration in the element lift. 16.The method according to claim 1, wherein the control controller judgesthat the electronically controlled thermostat has malfunctioned in casesa measurement of a resistance value of the thermo-element at a time thatthe engine is started indicates that a difference between the resistancevalue and a pre-stored reference resistance value is equal to or greaterthan a specified value.
 17. The method according to claim 14, whereinthe control controller predicts a radiator flow rate by detectingparameters which is at least one of an amount of element lift, atemperature of a heat generator, and a temperature of a temperaturesensor.